This research project is designed to identify the neuronal response to noxious stimulation of the periphery and nerve injury. Neurons in the dorsal root ganglion and spinal cord represent the first level of processing of neuronal information from the periphery. Using cellular and molecular techniques it is possible to identify important elements in the neuronal networks that subserve the response to nociception, nerve injury and regeneration. Calcium binding proteins (CBP) play an important role in cellular homeostasis and excitotoxicity related to ionic changes that occur in response to stimulation. Several different CBPs are found in the spinal cord. A comparison of their localization was undertaken in an effort to identify those related to nociceptive inputs or nerve injury. In the dorsal horn, calbindin D-28K (CB) is predominant in laminae I while calretinin (CR) is unique to laminae V and VI and calmodulin (CM) is densely distributed in lamina IX. In lamina II, both CB and CR are similarly distributed. CM which has been hypothesized to be important in the nitric oxide cascade, is not significant in the superficial dorsal horn, an observation in contradiction to that predicted by nitric oxide localization. The laminar localization of each CBP suggests that multiple CBPs are involved in the dorsal horn response to noxious stimulation and nerve injury. Nitric oxide (NO) has been proposed as a novel neuronal messenger involved in either cell protection or excitotoxicity. Because of the instability of NO, localization of the synthetic enzyme, nitric oxide synthase (NOS), with either antibodies, NADPH histochemistry or molecular probes has been used to study NO. Previous work in our laboratory has identified an induction of NOS mRNA in DRG after sciatic nerve cut. We further examined this effect in rats neonatally treated with capsaicin (CAP) to destroy a subpopulation of small-sized nociceptive DRG neurons. CAP is thought to act through a Ca2+ dependent excitotoxicity. Our studies demonstrated that most NO containing DRG neurons are capsaicin-sensitive and that the presence of NO does not protect the neurons from capsaicin induced excitotoxicity.